Ferrite circulators typically have a metal waveguide housing and dielectric transformers therein that serve as impedance-matching elements to provide an impedance match between air-filled input waveguides and a ferrite loaded junction region. An adhesive is typically used to bond the transformers to the waveguide housing of the circulators. The transformers commonly span the full waveguide height such that they are line-to-line with the waveguide floor and ceiling (or cover) minus the thickness of the adhesive. This structure can create a problem as some circulator assemblies may have transformers that protrude above the height of the waveguide due to transformer tolerances and/or assembly variation, preventing an interference fit.
When a transformer protrudes slightly beyond the waveguide height and a waveguide cover is put in place using fasteners, pneumatic presses, or laser-welding, the transformers can fracture due to interference. In using pneumatic presses to apply tuning covers, the transformer fracturing can occur even when the transformer does not protrude above the waveguide height due to slight bowing in of the cover from the applied pneumatic force.
When a transformer fractures, the unit has to go back to assembly to be re-worked causing delays and increased costs. If the circulator was tuned prior to the transformer fracturing, then the circulator typically has to be re-tuned after the re-work.